1. Field of the Invention
This invention relates to fuel pressure control valve devices, and more particularly to a fuel pressure control valve device effective in regulating pressure of fuel fed to an injection valve used in a fuel injection system for a vehicle.
2. Related Art Statement
In a vehicle such as an automobile, a fuel pressure control valve device is used as a device for controlling pressure of fuel fed to a fuel injection valve to a predetermined level. For example, this device is constructed such that pressure of fuel fed to the fuel injection valve is regulated in accordance with intake air pressure and a fuel flow rate injected through the fuel injection valve is always kept adjusted for the operating conditions.
Heretofore, there has been known a fuel pressure control valve device in which a sphere is used as a valve body of a control valve as disclosed in Japanese Utility Model Laid-Open No. 53-44325 and Utility Model Publication No. 62-24145.
As shown in FIG. 10, a valve body of sphere 6 is disposed between an armature 2, which is supported by a diaphragm 1 and movable in a fuel chamber, and a pole 3, in which a fuel passage 4 is formed for leading the fuel in the fuel chamber to a fuel discharge port. The sphere 6 is mounted in or demounted from a valve seat 5 formed in the intermediate portion of a fuel passage 4, in accordance with the movement of the armature 2, thus the fuel passage 4 being opened or closed. With this arrangement, the control valve can be simplified in construction.
However, in the conventional fuel pressure control valve device as shown in FIG. 10, the sphere 6 tends to be shifted laterally and to miss the place when the sphere 6 is moved in the valve seat 5 by the biasing force of a spring 7 for constantly urging the sphere 6 against the armature 2, thus resulting in inferior flow rate-pressure characteristics. In other words, a fuel commensurate with the pressure may not be discharged. This is because the sphere 6 is inserted in the conical valve seat 5 to be mounted thereto or demounted therefrom.
Another type of conventional fuel pressure control valve device is shown in FIG. 11. This valve device is constructed such that a valve seat 5a is formed of a circular edge, a conical guide hole 8 is formed on the armature 2, and the sphere 6 can be mounted in the valve seat 5A or demounted therefrom in a state of being inserted in the guide hole 8.
However, even with this fuel pressure control valve device, the sphere 6 tends to be shifted laterally and thus to miss the place when the armature 2 moves, thereby presenting the disadvantage of inferior flow rate-pressure characteristics similarly to the one shown in FIG. 10. In other words, the fuel flow rate commensurate with the pressure may not be attained.
Therefore, to obviate the problems, it can be proposed, as shown in FIG. 5, to form a fuel passage 34' in the top portion of the valve seat for slidably receiving a sphere 38' and guiding the sphere, and to form a plurality of longitudinal channels 39' as auxiliary fuel passages. The channels 39' are cuttingly provided in the side wall of the fuel passage 34', for preventing the lateral shift of the sphere and securing satisfactory flow of the fuel.
However, it has been made clear by the inventor of the present invention that, when the longitudinal channels 39' are provided along the normal lines, as shown in FIG. 5, fuel flows which have passed through these longitudinal channels 39' run against one another, thus causing turbulent flows as indicated by broken line arrows, thereby resulting in inferior flow rate-pressure characteristics. This phenomenon is remarkable, in particular, during a high flow rate.
Another undesirable aspect of the conventional device is pointed out as follows.
As a conventional fuel pressure control valve device, there is a fuel pressure control valve device comprising: a case constituting therein a fuel chamber and a pressure chamber; a fuel introducing port and a fuel discharge port, which are both opened on the side of the fuel chamber of the case; a pressure introducing port opened on the side of the pressure chamber of the case; a diaphragm stretchingly provided between the fuel chamber and the pressure chamber so as to divide the interior of the case into two chambers; an armature supported by the diaphragm and inserted into the fuel chamber; a coil spring provided in the pressure chamber so as to bias the armature toward the fuel chamber; a pole provided so as to form therein a fuel passage for leading the fuel in the fuel chamber to the fuel discharge port of the case; and a valve body disposed between the pole and the armature, for opening or closing the fuel passage in the pole in accordance with the movement of the armature.
In the above-described fuel pressure control valve device, the end of the coil spring on the side of the armature is received by a spring seat, and this spring seat is brought into abutting contact with the top surface of the diaphragm so as to be joined with the armature, so that the spring seat can be moved integrally with the diaphragm and the armature.
However, in the above-described fuel pressure control valve device, if the spring seat has a small diameter, then the diameter of winding of the coil spring becomes small, whereby a spring constant is raised to have an unfavorable pressure gradient, thereby lowering a rate of damping, or, in other words, lowering efficiency of pulsation absorptive action of the fuel pressure control valve device. On the other hand, when the spring seat is formed to have a large diameter, an allowance for deformation of the diaphragm comes to be small, thereby, also lowering the rate of damping.